Generally, high ratio zoom lens use more than four optical lens groups, and at least two groups are movable. Because of the two moving groups, the design limitation of zoom lenses is severer, the optical design is more difficult, and the optical quality is hard to improve. On the other hand, though using more than two moving lens groups in the zoom lens may improve the freedom of optical design and improve the optical quality, it actually also adds the difficulty and cost of mechanical design. Conventional four-lens-group zoom lens with two moving groups uses two motors to drive a zooming lens group and a focus lens group respectively. Conventional four-lens-group zoom lens with three moving groups uses a cylindrical cam to move two zooming lens groups, and a motor to drive the focus lens group. The above mechanisms are complicated, the component fabrications are difficult and the costs are high.
Different kinds of zoom lenses are disclosed in U.S. Pat. Nos. 4,636,041, 4,948,235, 5,140,468, 5,298,933, 5,570,149, 5,627,683, 5,636,062, 5,689,739, 5,708,535, 5,790,908 and 6,031,998. A part of them are technically reviewed as follows.
U.S. Pat. No. 5,140,468 discloses a zoom lens of four lens groups, in which three groups are movable. Two planar cams driven by two motors control the relative positions of the three moving lens groups. Because the moving directions of the planar cams are perpendicular to the optical axis, they occupy much space and are hard to be miniaturized.
U.S. Pat. No. 5,298,933 discloses a zoom lens of four lens groups, in which the first group and the third group are fixed groups; the second group and the fourth group are moving groups respectively driven by a motor. It has advantages of simple structure and low cost. However, the second group and the fourth group use different rails, and the optical design is also strict.
U.S. Pat. No. 5,627,683 discloses a zoom lens of four lens groups that are all moving groups. Each moving group is actuated by a cam ring or a thread ring, the mechanism is complicated and costs high.
U.S. Pat. No. 5,636,062 discloses a zoom lens of four lens groups. It uses a crank member to drive two lens groups.
U.S. Pat. No. 5,689,739 discloses a zoom lens of four lens groups. It uses a specific drive mechanism including a cam lever and two cam pins. The drive mechanism is hard to be miniaturized.
U.S. Pat. No. 5,708,535 discloses a zoom lens of four lens groups, in which the first group and the third group are fixed groups; the second group and the fourth group are moving groups respectively driven by a motor. It has advantages of simple structure and low cost. However, the second group and the fourth group use different rails.
U.S. Pat. No. 6,031,998 discloses a zoom lens of four lens groups, in which the actuator is a cylinder. The guide rail in the cylinder is not easy to be made.